brake fluid?

In my bike manual, it is recommended that you use the same brake fluid as whats in the system prior, and im not sure what either bike has in them, niether are the previous owners. whats my best option? if i bleed another brake fluid through, will that clear the lines of the old stuff?

It should. You should be fine if you use DOT 3 or DOT 4 brake fluid unless the previous owner screwed up and used silicone (DOT 5) fluid. Thankfully, the odds are he did not. Just bleed until nice fresh fluid with no bubbles comes through. Ed

ED a wise man.....I agree, just keep flushing the system untill you feel the gook is out. I would use dot 3. rem that this stuff will eat the finish off parts....dont get on any paint, powdercoat and so on.....dont get on skin,

This is a long read, but touches on differences of DOT 3 and 4 brake fluid, and what happens when DOT 5 fluid is used:




DOT 3 VS DOT 4 Brake Fluid

I just flushed my brake lines with new DOT 3 fluid only to find out that the master cylinder has a leak. Instead of rebuilding the master cylinder, I bought a 'newer' used MC off of ebay, but it calls for DOT 4 instead of DOT 3! D'oh! Well, I've heard that 3 & 4 are very similar and I'm wondering how thoroughly I need to flush the DOT 3 fluid out of the brake lines? Can I just 'push' the DOT 3 fluid out by adding DOT 4 to the master cylinder and pump until I think I have all of the DOT 3 out of the lines? How would you do it?

...Can I just 'push' the DOT 3 fluid out by adding DOT 4 to the master cylinder and pump until I think I have all of the DOT 3 out of the lines? How would you do it?

YES. That method is just fine. Same for the routine "flushes" without requiring re-bleeding from scratch.

I use a rubber squeeze syringe to remove most of the existing reservoir fluid, but leaving the bottom ports covered with fluid so as to avoid air entering the line. Then fill with new fresh fluid, pump it through (always leaving the bottom ports covered with fluid so as to avoid air entering the line) and repeat refilling and pumping until the new fresh fluid exits the bleeder valve.

Patton

Brake Fluid Problems

"I like to go with DOT 5 fluid when I rebuild the brakes, just a better product"/quote]

Maybe not better, but certainly different. An alarm went off in my brain, so I Googled this up.

"More than you ever wanted to know about brake fluid....

Brake fluid facts

By Steve Wall
As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows:

Fluid compatibility with the brake system rubber, plastic and metal components.

Water absorption and corrosion.
* Fluid boiling point and other physical.
* Brake system contamination and sludging.

Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene.

First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry .


Fluid Compatibility
Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components, such as caliper piston boots, which are attacked by silicon fluids and greases.

Water absorption and corrosion
The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense.

Fluid boiling point
DOT 4 glycol based fluid has a higher boiling point (446°F) than DOT 3 (440 ºF), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500°F) however if water got into the system, and a big globule found its way into a caliper, the water would side at temperatures very much below freezing, let alone at 40° below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances.

With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas.

Brake system contamination
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some car owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Older brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

New developments
Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446°F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation -which exhibit a minimum dry boiling point of 500°F (same as silicone, but different chemistry).

Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590°F. It is miscible with DOT 3-4 fluds but has yet to see commercial usage." I learned in the past thru others mistakes not to switch to DOT 5 in systems designed for DOT 3 or 4.

If the current fluid is purple it is DOT 5. Dot 5.1 is not silicon, i think it is just less vicous than 3 and 4 for use in ABS systems. If you are replacing brake lines and rebuilding the MC and caliper it would be a good time to switch to DOT 5. I like it in older bikes because it won't eat the paint and corrode everything near the MC. It doesn't need to be changed as often as 3 and 4, but as mentioned earlier if water does enter the system it will settle in the bottom of the caliper. Mfolks article pertains more to autos. FYI Harley uses 5 in its bikes.

DOT 5 won't eat paint; true. However, it should be changed at least if not more often than DOT3 or DOT4. DOT 3 & 4 absorb water. This may sound like a negative, and if brake fluid changes are neglected long enough it can reduce the boiling point of the brake fluid, but it actually has a positive aspect. That is, the moisture that enters the brake system (moisture enters ALL brake systems regardless of the fluid type) is absorbed into the fluid and is evenly distributed within the brake system. This reduces the concentration of water in any one area. DOT-5 silicone brake fluid (not to be confused with DOT 5.1) will not absorb water, so the moisture that enters the brake system is not evenly distributed. Instead, it forms "puddles" of water. These puddles may settle in the lowest sections of the brake system, and being pretty much pure water can create rust if they are in contact with steel components. Since all brake systems absorb water they all need to have the brake fluid changed periodically.

Racers often prefer DOT-5 because its boiling point is higher than that of DOT 3 or 4, so it may meet the demands of the extreme braking conditions and subsequent high temperatures encountered in racing. That is a good thing for racers buy not really relevant for street use. The DOT-5 water puddling issue is less of a problem in racing where the brake fluid is normally changed much more frequently than in regular street use so puddling doesn't have much chance of forming. DOT 5 does have another disadvantage in that it it more compressible than DOT 3 or DOT 4. This is not a noticeable issue on most bikes, but it is why DOT-5 must not be used in vehicles with ABS systems.

I suspect Harley likes DOT 5 primarily because it will not destroy the bike's paint when their crappy brake lines wear through and spew the brake fluid all over the bike. This is what happened with my best friend's $25+k Ultra-Glide when the rear brake line wore through by rubbing on the frame under the bike. I suggested he encase the replacement line in a spring like that which came standard on my 35 year old KZ650-C1.

One thing to keep in mind is that DOT-5 fluid must not be mixed with any other type DOT fluid or the brake system will be fouled. Ed

Any brake fluid should have the trash flushed out of it atleast once every season no matter what it is.
And yes Ive used dot5 fluid in just about every kind of vehicle under the sun in last 30 years without issue,just like anything else it comes down to maintenance.

awesome thanks all! and is it bad to put synthetic oil in the older bikes?

Been around mobil 1 synthetic used in cars since 78,been a fan of golden spectro synthetic for bikes since around 81-82.
People said it would hurt bike clutches 30 years ago,but Ive yet to see a clutch related problem from it.
Seems like most of the people who say things dont work have never actually used/tried them,they read something on the internet so it must be true! :woohoo:
Best advice I can give anybody about anything is to try it for yourself and see how it works for you.
One thing I can tell you is make sure you have good gaskets when using synthetic oil! :laugh:

I've been using Mobil-1 Racing 4T fully synthetic MOTORCYCLE oil in my KZ650-C1 for 6 years. It works great. Whatever oil you choose make sure the container states that it meets the JASO-MA standard as this is the standard for motorcycle engines with wet clutches (like the KZ engines). There are numerous oils, synthetic and non-synthetic that meet this standard. Ed